1. Field of the Invention
The present invention relates to a device for separating a mixture of gas and liquid, this mixture being formed particularly by hydrocarbons, at the intake of a pump connected to the bottom end of a tubular column at the bottom of a drilled well.
After the positioning of wells drilled towards the reservoir of the geological formation, hydrocarbon production installations use pumping systems to raise the oil to the surface. For this operation, a tubular column is lowered into the drilled well serving as a pipe for producing the hydrocarbons at the end of which is disposed a pump.
2. Description of the Prior Art
The pumps used may be of different types: piston pumps, centrifugal pumps, hydraulic pumps, beam pumps, rotary positive displacement pumps (commercially called "MOINEAU" pumps).
Although such pumps operate satisfactorily when the pumped fluid is formed for the most part of liquid, problems arise and develop when a volume of free gas is mixed with the production fluid. In fact, if the intake pressure of a fluid to a pump is less than the bubble point pressure above which all the gas is dissolved in the oil, pumps intake free gas mixed with the production fluid.
Under these conditions, the result is a low pumping efficiency if the flowrate measured from the reservoir is related to the theoretical delivery of the pump and acceleration of the working of the pump affecting the increase of the speed of rotation for piston pumps.
The prior art, illustrated by the two patents, GB 983 644 and U.S. Pat. No. 2,969,742, have solved this problem by using a gas/liquid separation device mounted around the pump for limiting as much as possible the presence of gas in suspension in the liquid during working of the pump. The pump is introduced at the bottom of a tubular pipe which is closed at its lower part and provided with intake orifices at its upper part so that, at the level of the orifices of the separator, the free gas tends to be removed to the surface, whereas the oil is sucked in by the pump.
However, such an assembly has a serious drawback which corresponds to the dry operation of the pump when the liquid level does not reach the intake orifices.
The most harmful effect is found in a reduction of the useful life of positive displacement pumps of MOINEAU type in which the gas introduced tends to filter into the elastomer of the stator and so deform the inner helical gears of the pump. In other types of pump, the wear is amplified by a risk of blockage of the pump.